NAME
    Error::Show - Locate and Diagnose Errors/Exceptions in Perl programs

SYNOPSIS
  String EVAL
    Consider the string/program to be evaluated that has a illegal divide by
    zero ( or could be a syntax error );

      use Error::Show;

      my $prog='

      sub call_me {
        $a+1/0;
      }

      say "hello there";
      call_me;

      ';

    With normal string eval and exception checking, we get:

      my $result =eval $prog; 
      if($@){
        say $@;
      }
      #======== OUTPUT

      hello there
      Illegal division by zero at (eval 1) line 4.

    Using normal string eval with "context" we get:

      my $result =eval $prog; 
      if($@){
        say "ERROR is $@".Error::Show::context $@;
      }

      #====== OUTPUT

      (eval 2)
      Illegal division by zero at (eval 2) 0
          examples/eval.pl
          30
          31   {
          32     say "================== Normal string with context =====================";
          33     my $result =eval $prog;
          34     if($@){
          35=>     say Error::Show::context $@;
          36     }
          37
          38   }
          39
          40

    Using "streval" with "context" we get:

      my $result =eval {streval $prog};
      if($@){
        say Error::Show::context $@;
      }

      #======= OUTPUT

      hello there
      (eval 4)
      1
      2
      3     sub call_me {
      4=>     $a+1/0;
      5     }
      6
      7     say "hello there";
      8     call_me;
      9
      Illegal division by zero at (eval 4) 4
          examples/eval.pl
          41
          42   say "";
          43
          44   {
          45     say "================== eval streval =====================";
          46=>   my $result =eval {streval $prog};
          47     if($@){
          48       say Error::Show::context $@;
          49     }
          50
          51

  Command Line Syntax Checking
    Consider the following program (at examples/synopsis.pl in this
    distribution). It has a syntax error on line 13, and uses an
    experimental feature on line 7.

      use strict;
      use warnings;
      use Time::HiRes;

      use feature "refaliasing";

      \my $a=\"hello";
      my $time=time;
      for(1..1000){
        print "$_\n";
      }

      my $crazy-var=2;

      use Socket;

      print "this will never work";

    Attempting to run this program with Perl normally gives this error
    output:

      ->perl examples/synopsis.pl       
      Aliasing via reference is experimental at examples/synopsis.pl line 7.
      Can't modify subtraction (-) in scalar assignment at examples/synopsis.pl line 13, near "2;"
      BEGIN not safe after errors--compilation aborted at examples/synopsis.pl line 15.

    With "Error::Show" enabled with the "-M" switch, this instead looks like
    this:

      ->perl -MError::Show=warn  examples/synopsis.pl
      examples/synopsis.pl
       3   use Time::HiRes;
       4
       5   use feature "refaliasing";
       6
       7=> \my $a=\"hello";
       8   my $time=time;
       9   for(1..1000){
      10    print "$_\n";
      11   }
      12
      Aliasing via reference is experimental at examples/synopsis.pl line 7.
      examples/synopsis.pl
       9   for(1..1000){
      10    print "$_\n";
      11   }
      12
      13=> my $crazy-var=2;
      14
      15   use Socket;
      16
      17   print "this will never work";
      Can't modify subtraction (-) in scalar assignment at examples/synopsis.pl line 13, near "2;"
      examples/synopsis.pl
      11   }
      12
      13   my $crazy-var=2;
      14
      15=> use Socket;
      16
      17   print "this will never work";
      BEGIN not safe after errors--compilation aborted at examples/synopsis.pl line 15.

  Command Line Exception Call Stack Dump (from v0.4.0)
    Consider the following short program (examples/synopsis2.pl

      use v5.36;

      sub test {

        my $a=1/0;
      }


      test;

    Running this program with Perl normally gives this error output:

      perl examples/synopsis2.pl  
      Illegal division by zero at examples/synopsis2.pl line 5.

    With "Error::Show" enabled with the "-M" switch, this instead looks like
    this:

      perl -MError::Show examples/synopsis2.pl
      examples/synopsis2.pl
      1   use v5.36;
      2
      3   sub test {
      4
      5=>   my $a=1/0;
      6   }
      7
      8
      9   test;
      Illegal division by zero at examples/synopsis2.pl 5

          examples/synopsis2.pl
          4
          5     my $a=1/0;
          6   }
          7
          8
          9=> test;
      Illegal division by zero at examples/synopsis2.pl 5

  In Program
    Use at runtime to supplement exception handling without signal handler
    modification:

      use Error::Show;

      #an die caught in a try/eval triggers an exception

      # No argument uses $@ as error
      #
      eval { exceptional_code };
      say STDERR context if $@;


      # or a single exception argument of your choosing
      #
      use v5.36;
      try { 
        exceptional_code
      }
      catch($e) {
        say STDERR context $e;
      }

      # Show context down a stack

      try {

        Some_execption_class->throw("Bad things");

      }
      catch($e){
        say STDERR context $e;
      }

DESCRIPTION
    This module provides three tools/modes to help locate and diagnose
    errors in your Perl programs.

  Command Line
    From the command line this module transparently executes your
    syntactically correct program. No code changes are required. However in
    the case of syntax errors (or warnings if desired), it extracts context
    (lines of code) surrounding them. The lines are prefixed with numbers
    and the nicely formatted context is dumped on STDERR for you to see the
    error or your ways.

    The resulting output is optionally filtered seamlessly through the
    splain program (see diagnostics), giving more information on why the
    reported syntax errors and warnings might have occurred.

  In Program Exception Context
    From within a program, this module can be used to give formatted code
    context around the source of an exception and the context of each of the
    stack frames captured when the exception was raised.

    It supports Perl string exceptions and warnings directly and also
    provides the ability to integrate third party CPAN exception objects and
    traces with minimal effort. Please see examples in this document or in
    the examples directory of the distribution showing use with
    Mojo::Exception, Exception::Base, Exception::Class::Base and
    Class::Throwable.

    From "v0.5.0" a "throw" routine is exported which, generates a very
    basic exception object, with stack frame capture, in case using an
    larger exception object/class is unneeded

  String evals with Execption/Syntax Error Context
    From "v0.5.0" the "streval" subroutine has been added to allow context
    information to be generated for errors originating from code dynamically
    created from string evaluations.

Changes and Options
    A handful of options are available for basic configuration of how many
    lines of code to print before and after the error line, indenting of
    stack trace context, etc.

    v0.5.0 Has alot of changes which might break compatibility. THe up side
    is the codes is simpler, has less errors, and easier to use. This is
    especial the case for third party exceptions objects. It also gives the
    intended purpose of handling errors and exceptions from string evals
    like any other.

    That being said, an earlier version might need to be used if you want
    the use the $@ variable implicitly in a call to "context". This
    subroutine now requires an explicated error argument

    Sub routines "context", "throw" and "streval" are exported by default.

    From v0.3.0: "context" subroutine is now exported by default. To prevent
    this, import with an empty list, ie "use Error::Show ()".

    "From v0.2.0:", Added 'advanced string eval' support has been added for
    better context reporting of dynamically generated code.

USAGE
  Command Line Usage (Syntax check and Exception Catching)
            perl -MError::Show  [options] file.pl

    When included in a command line switch to Perl, "-MError::Show" syntax
    checks the input program. If the syntax is OK, normal execution
    continues in a transparent fashion. Otherwise, detailed code context
    surrounding the source of the error is generated and printed on STDERR.

    From v0.4.0 a global __DIE__ handler is also installed, which will catch
    any stray exceptions during execution and present a line numbered
    summary stack trace. Programs a free to overload this handler. However
    the features of this module will be lost.

    NOTE: It is important that it's the first "-M" switch for this module to
    operate correctly and to prevent any incompatibilities withe global
    signal handlers.

    If the -c flag is specified, only a syntax check will be performed,
    mimicking normal Perl behaviour.

    Additional @INC directories using the -I switch are supported as are
    additional modules via the -M switch.

   CLI Usage Options
    The following options can be used in isolation or together:

   clean
    If you prefer just the code context without the Perl error, add the
    clean option:

      perl -MError::Show=clean file.pl

   warn
    This options enables processing of warnings as well as errors.

      perl -MError::Show=warn file.pl

   splain
    Runs the output through the splain program (see diagnostics), giving
    probable reasons behind the error or warning

      perl -MError::Show=splain file.pl

   no_handler (from v0.4.0)
      perl -MError::Show=no_handler file.pl

    Prevents the global DIE handler from being installed.

   Return code
    When in check only mode (-c), the main process is exited, just has Perl
    normally would have done. The return code is a replica of what Perl
    would have reported for success/failure of a syntax check.

  In Program (Exception) Usage
    Simply bring Error::Show into your program with a use statement:

      use Error::Show;

    It provides a single subroutine for processing errors and exceptions.

   Error::Show::context
      my $context=Error::Show::context $error , options_pairs, ...;

    Takes an error string, or exception object $error and extracts the code
    surrounding the source of the error. The code lines are prefixed with
    line numbers and the error line marked with a fat arrow.

    The expected types of error are

    Error string, as per "die" and "warn"
        This is expected to contain file and line number. These are
        extracted from the string error to locate context.

    Supported Execption Object
        Several common exceptions classes on CPAN are supported:

        Error::Show::Exception
        Exception::Class::Base
        Exception::Base
        Class::Throwable
        Mojo::Exception

        Other classes will likely work as long as the stringify to resemble
        a perl error string (with the filename and line number formatted
        correctly). The stack frame capture would work however)

    The return value is the formatted context, followed by the original Perl
    error strings, or stringified exception objects/messages:

      filename.pl 
      10  #code before 
      11  #code before 
      12=>#this line caused the error
      13  #code after
      14  #code after

      ... error... at filename.pl line 12 ...

    The "context" subroutine (5) is exported by default, so does not need a
    fully qualified name

    "context" Can also be called with package arrow notation (6) ie
    "Error::Show->context(...)" if prefered, with the same argument handling
    as the other forms.

    Options include:

   limit
      limit=>$int

    From v0.2.0: Limits the number of errors to extract and generate context
    for. Default is 100. If <=0, no limiting is applied all all errors are
    processed.

   depth
      depth=>$int

    From v0.5.1: Limits the level of frames reported. Default is unlimited.
    If <0 or not defined. 0 is the current frame

   reverse
      reverse=>$bool

    From v0.2.0: Reverses the order of error processing.

    Perl type string errors are sorted and processing in ascending line
    number order. When this option is used, the lines are processed by
    descending line number first. Does not change order of files processed.

    If frames are used instead, they are processed in reverse order to how
    they where supplied when this option is in effect.

   pre_lines
      pre_lines=>value

    Specific the maximum lines of code to display before the error line.
    Default is 5.

   post_lines
      post_lines=>value

    Specific the maximum lines of code to display after the error line.
    Default is 5.

   clean
      clean=>bool

    When true, the normal Perl error string is not included in the context
    information, for a cleaner look.

   indent
        indent=>string

    The string to use for each level of indent when printing multiple stack
    frames. Defaults to 4 spaces.

   splain
        splain=>1

    The resulting output will be filtered through the splain program.

   program
        program=>$prog

    The program option is used to specify the program text to process when
    there is no actual file. This is needed when to show syntax errors in a
    string "eval":

        my $prog='my $a="This will Fail"+b';
        eval $prog;
        if($@){
          say Error::Show::context error=>$@, program=>prog;
        }

    For advanced string eval processing options please see the ADVANCED
    STRING EVAL section in this document.

   streval
      local $@;

      my $result=eval { streval "program";

      if($@){
        print STDERR context $@;
      }


      ##### or ####


      try {
        my $result=strval "program";
      }
      catch($e){
        print STDERR context $e;
      }

    "streval" makes it possible to debug code generated from string eval.
    Internally it caches program code, to allow a context to be generated in
    the case of an exception.

    NOTE: It also throws an exception on syntax error, which also then can
    have a context generated for it.

   throw
      throw "My error message";

    Raises an exception with a basic exception object with the provided
    message. Captures the call stack frames at the point of call.

    Use this if you don't want to use other exception classes/modules

ADVANCED STRING EVAL
    From v0.2.0 features to support advanced string evaluation are
    available. This was added to support the error reporting needs of the
    Template::Plex module.

    Consider the following example. The 'meat' is the sub in the middle of
    the string. Any errors/context reported should be relative to this, not
    the start of the overall eval string. With some help from comment
    markers "##_PREAMBLE" and "##_POSTAMBLE", when can search for the middle
    and rebase the error line numbering.

      eval {
        "my $some_prep_work=1;
        call_somthing();
        #comments...
    
        ##_PREAMBLE

        sub {
           #code generated from user input...
           say "My really cool dynamically created code"
        }

        ##_POSTAMBLE

        #More code 
        #Cleanup stuff.
        "
      }

    Additional configuration options can be provided to search for the
    relevant code lines and offset the error line numbers.

    NOTE if these options are used, the message field is modified with
    updated line numbers if its in the form of a normal Perl errors ie
    'error line 123 at file'.

   start_mark
      start_mark=>$regexp

    If specified, is a used as a regexp to match against source code lines.
    The line after a successful match is now the first line.

    This allows inserting a special marker to indicate the start of 'code of
    interest' with out knowing the exact line number in the resulting code.

    This is undefined and unused by default.

   end_mark
      end_mark=>$regexp

    If specified, is used as a regexp to match against source lines, in
    reverse order. The line after a successful match is now the last line

    This allows inserting a special marker to indicate the end of 'code of
    interest'.

    This is undefined unused by default.

   start_offset
      start_offset=>$int

    A static offset to add to the start line (which may have been modified
    by the start_mark option). The result will be classed as the minimum
    line number of the file/string.

    This is useful to prevent any preamble after the start_mark line in your
    string eval showing up in the user program context.

   end_offset
    A static offset to subtract to the end line (which may have been
    modified by the end_mark option). The result will be classed as the
    maximum line number of the file.

    This is useful to prevent any postamble before the end_mark in your
    string eval showing up in the user program context.

FUTURE WORK/TODO
    Possible just use the DIE and WARN signal handler instead of forking
    processes?
    Make usable from a Language Server?
    Colour terminal output?
    JSON output?

KNOWN ISSUES/GOTCHAS
    Checking/running programs via STDIN, -e and -E switches is not supported
    and will die with an error message.

    More data then needed is pushed through the splain program when splain
    option is used, which isn't ideal.

SEE ALSO
    Perl::Syntax provides syntax checking from the command line. However it
    doesn't show any errors by design (only interested in process return
    code)

    Syntax::Check provides programmatic syntax checking of files.

    Perl::Critic gives actual Perl linting, but not great for syntax errors.

    diagnostics and the "splain" program give some very useful explanations
    about the otherwise terse error strings normally output. It is part of
    the Perl distribution

AUTHOR
    Ruben Westerberg, <drclaw@mac.com>

REPOSITORTY and BUGS
    Please report any bugs via git hub:
    <https://github.com/drclaw1394/perl-error-show>

COPYRIGHT AND LICENSE
    Copyright (C) 2025 by Ruben Westerberg

    This library is free software; you can redistribute it and/or modify it
    under the same terms as Perl or the MIT license.

DISCLAIMER OF WARRANTIES
    THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
    WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
    MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

